1. Field of the Invention
The present invention relates to a light emitting diode, especially to a method of manufacturing light emitting diode device that isolates a light-emitting side from other regions of the semi-manufactured LED device, such as a wire-bonding region, for coating phosphors on the light-emitting side alone.
2. Description of the Related Art
Light-emitting diodes (LED) are forward-biased P-N junction diodes made of semiconductor materials. When terminals of the PN junction diodes are biased in a forward direction, the recombination of non-equilibrium carriers (electron-hole pairs) causes an emission of light. Foregoing light-emitting process primarily corresponds to a spontaneous light-emitting process. Materials for manufacturing the LED are heavily doped and therefore form a PN junction wherein an n-type region has an excess of free electrons and a p-type region an excess of holes under a thermal equilibrium condition. A depletion region forms spontaneously across a P-N junction and prevents electrons and holes from recombining. When the p-n junction is forward-biased with a sufficient voltage, the depletion region will be narrowed and electrons can overcome a resistivity of the depletion region to cross the PN junction and inject into a side of the PN junction near the p-type region. Electrons then meet and recombine with holes and the recombination thereby results in light emission.
Generally, a conventional light-emitting diode (LED) is manufactured by forming a laminated structure mounted on a substrate wherein the laminated structure comprises an n-type semiconductor layer, a light-emitting layer and a p-type semiconductor layer. The conventional LED may adopt different materials and structures to meet different desired wavelengths of emitted lights. For example, blue and green LEDs usually use sapphire as a substrate and GaInN epitaxial structure as a laminated structure. Because the sapphire is used as the substrate, an anode and a cathode of the conventional light-emitting diode are formed at the same side of the substrate. As reference to FIG. 1, an n-type GaN layer (5), a light-emitting layer (4), a p-type GaN layer (3) and a transparent electrode layer (2) are sequentially formed on a sapphire substrate (6). An anode (1) and a cathode (7) are respectively formed on the transparent electrode layer (2) and the n-type GaN layer (5). However, the sapphire substrate (6) is weak at heat dissipating and a heat-conductive structure is disposed at a distance from the light-emitting layer (4). Therefore the conventional LEDs are limited to be manufactured into small-area ones with low power, such as one LED having an area of 0.3 mm×0.3 mm with an operating current at 20 mA.
With the requirements of a higher lighting efficiency and better illumination, a conventional LED device having a flip chip structure gradually replaces foregoing conventional LED device as a high power LED device. With reference to FIG. 2, a back side of a flip-chip (8) functions as a light-emitting side, and electrodes at a front side of the flip-chip (8) is attached to a heat-sink side of a silicon substrate (9) wherein the silicon substrate (9) functions as a heat-conductive structure. Since the flip-chip (8) are close to the silicon substrate (9), a heat-dissipating efficiency is enhanced. Therefore, area of an LED device can be increased to 1 mm×1 mm, operating current can be achieved to 300 or 500 mA and then the LED device can be provided with a power up to 1 Watt.
High power LED devices are mainly applied to white light illumination. A technique of manufacturing white LED devices usually requires a package technique of packaging phosphors. However, during a process of manufacturing white LED devices, phosphor coating is hard to control and uneven white light illumination may occur to influence color temperature and coordinate of emitted white lights, and thereby lead to a package yield decrease. Such package defect is particularly obvious to a high power white LED device.
To overcome the shortcomings, the present invention provides a method of manufacturing light-emitting diode device to mitigate or obviate the aforementioned problems.